A pixel (an abbreviation of pictures) can be considered as one of the many tiny dots that make up the representation of a picture in a computer's memory. However, each such information element is not really a dot, nor a square, but an abstract sample. With care, pixels in an image can be reproduced at any size without the appearance of visible dots or squares; but in many contexts, they are reproduced as dots or squares and can be visibly distinct when not fine enough. The intensity of each pixel is variable; in color systems, each pixel has typically three or four dimensions of variability such and red, green and blue, or cyan, magenta, yellow and black.
Pixels are generally thought of as the smallest complete sample of an image. The definition is highly context sensitive. For example, we can speak of pixels in a visible mage (e.g., a printed page) or pixels carried by one or more electronic signal(s), or represented by one or more digital value(s), or pixels on a display device, or pixels in a digital camera (photo sensor elements). This list is not exhaustive and depending on context there are several synonyms which are accurate in particular contexts, e.g. pel, sample, bytes, bits, dots, sports, superset, triad, stripe set, window, etc. We can also speak of pixels in the abstract, in particular when using pixels as a measure of resolution, e.g. 2400 pixels per inch or 640 pixels per line. “Dots” is often used to mean pixels, especially by computer sales and marketing people, and gives rise to the abbreviation DPI or dots per inch.
The more pixels used to represent an image, the closer the result can resemble the original. The number of pixels in an image is sometimes called the resolution, though resolution can also be defined more specifically. Pixels can be expressed as a single number, as in a “three-megapixel” digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a “640 by 480 display”, which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display), and therefore has a total number of 640×480=307,200 pixels.
In computer programming, an image composed of pixels is known as a bitmapped image or a raster image. The word raster originates from analogue television technology. Bitmapped images are used to encode digital video and to produce some types of computer-generated art. Since the resolution of most computer displays can be adjusted from the computer's operating system, a display's pixel resolution may not be an absolute measurement.
Modern LCD computer displays are designed with a native resolution which can be considered as the perfect match between pixels and triads (CRT displays are use red-green-blue phosphor triads, but they are not coincident with image pixels, and cannot therefore be said to be equivalent to pixels).
Typically, the native resolution will produce the sharpest picture capable from the display. However since the user can adjust the resolution, the monitor must be capable of displaying other resolutions. However, the size of the pixels on LCD displays are effectively fixed. As such, non-native resolutions have to be supported by approximate resampling in the LCD screen, using interpolation algorithms. This often causes the screen to look jagged or blurry. For example, a display with a native resolution of 1280×1024 will look best set at 1280×1024 resolution, and may be unable to display in 1600×1200 at all due to the lack of physical triads.
The aspect ratio of an image (“aspect ratio”) can be defined as its displayed width divided by its height (usually expressed as “x:y”). For instance, the aspect ratio of a traditional television screen is 4:3, or 1.33:1. High definition television uses an aspect of 16:9, or about 1.78:1. Aspect ratios of 2.39:1 (2.35:1 prior to SMPTE revision in 1970) or 1.85:1 are frequently used in cinematography, while the aspect ratio of a sync-sound 35 mm film frame is around 1.378:1 (also known as “Academy” ratio). Silent films which used the full frame were shot in 1.33:1.
Today, several different aspect ratios are used to display content (e.g., graphics). The aspect ratios may vary from display device to display device and from manufacturer to manufacturer and change as new devices come to market. Varying aspect ratios provide unique challenges in a highly regulated gaming environment. As such, techniques that can accommodate displaying content for various aspect ratios would be highly useful.